Load modulation arrangement

ABSTRACT

The present invention concerns a load modulation arrangement adapted to be connected to an amplifying device. The load modulation arrangement comprises a first reactive element, a second reactive element and at least one variable capacitive element. Further, the load modulation arrangement comprises a quarter wave transforming element adapted to be connected to the first reactive element. The present invention also concerns a method for load modulation, a wireless transceiver and a radio transmission device.

TECHNICAL FIELD

The present invention relates to the field of load modulationarrangements. More particularly the present invention relates to a loadmodulation arrangement as well as a method, a wireless transceiver and aradio transmission device comprising such a load modulation arrangement.

BACKGROUND

The rapid development of the telecommunications industry have madewireless handheld devices like cell phones, pagers, two-way messagingdevices, etc. massively popular, creating a need for new electroniccomponents and circuits in both mobile and base station systems ascompetition drives the introduction of expanded capabilities.

Radio frequency power amplifiers contribute to the power consumption inthe communications networks. One reason for this is the complexity ofwireless communication networks, with intense baseband signalprocessing. The major source of power consumption in a base station isthe base stations power amplifiers. The high power consumption of thepower amplifiers is mainly due to low mean efficiency where a lot of theinput power is converted into heat. This requires both costly and spacedemanding arrangements to allow for sufficient cooling of the system.

Also, the power consumption of the system reflects on other aspects suchas battery backup systems and the operators cost of power over thelifetime of the radio base station. All extra means needed to compensatefor high power consumption and low efficiency will accumulate on the endcustomer's price for the base station.

The low efficiency of the power amplifier is due to the amplifierworking under backed off conditions for most of the time. This isbecause a signal according to e.g. WCDMA has a high peak to averageratio. Inherently the efficiency of an amplifier is at its best when theamplifier is working close to saturation. For backed off conditions, theefficiency decays very fast with reduced output power.

Efficiency in back off denotes efficiency when an amplifier is usedbelow its maximum available output power. Back off is the difference indecibels between actual used output power and the maximum availableoutput power of the amplifier.

Thus, to reduce operating costs of base stations and extend battery lifein mobile units, there is a need to develop new amplifiers to replacethe traditionally inefficient, power wasting, elderly designs currentlyin use.

Many contemporary base station amplifiers employ complex techniques torealize amplifiers with a high degree of linearity over a broadfrequency range. Unfortunately those solutions have a low efficiencywhen working in power back off.

Handset power amplifiers also suffer from efficiency problems, oftenmore critical than those for base stations as the power supply formobile user equipment is strictly limited. Today's smaller, faster andmore effective portable electronics demand high power with minimizedlosses.

Load modulation networks have been suggested as feasible means ofmaintaining the efficiency of a power amplifier at reduced output power.This may be useful when the amplifier works on signals with a high peakto average signal amplitude, for example WCDMA signals.

An important characteristic of a load modulation network is the ratio ofinput impedance change in relation to the change of the tuning device.This will set the dynamic range of the load modulation network for agiven tuning device range. Designing the load modulation network withhigh dynamic range will severely deteriorate the bandwidth for a Pishaped load modulation network. A T-shaped network has a superiorbandwidth under all circumstances, compared with a Pi shaped network.

The bandwidth of the load modulation network can be substantiallyincreased by replacing the Pi shaped network with a T shaped network.The names Pi shaped network and T shaped network refer to the shapes ofthe respective load modulation networks.

However, the T shaped network has a relation of network input impedanceto tuning device capacitance inverse to that of the Pi network. Thisinverse relation of input impedance to tuning device capacitance createssome major drawbacks using a T shaped network. Some examples of suchmajor drawbacks are very high power dissipation in the tuning device anda very limited dynamic range, a few decibels (dB). The high powerdissipation is due to high values of Radio Frequency (RF) voltage at thetuning element node simultaneous as large values of capacitance. Thelimitation in dynamic range is due to the same mechanism. The biasvoltage to the tuning device can not be set to lower values, i.e. largecapacitance values since this would give a reverse voltage over thetuning device by the peaks of the Radio Frequency voltage. This couldpotentially destroy the tuning device, or give rise to severedistortion.

SUMMARY

The present invention aims at obviating or reducing at least some of theabove mentioned disadvantages associated with existing technology.

It is an object of the present invention to provide a load modulationnetwork with improved bandwidth and/or efficiency.

The object is achieved by a load modulation arrangement adapted to beconnected to an amplifying device. The load modulation arrangementcomprises a first reactive element, a second reactive element and atleast one variable capacitive element. Further, the load modulationarrangement comprises a quarter wave transforming element adapted to beconnected to the first reactive element.

The object is also achieved by a method for load modulation in anarrangement. The arrangement is adapted to be connected to an amplifyingdevice. The load modulation arrangement comprises a first reactiveelement. Further, the load modulation arrangement comprises a secondreactive element. Further yet, the load modulation arrangement comprisesat least one variable capacitive element. The method also comprises thestep of connecting a quarter wave transforming element to the firstreactive element.

The load modulation arrangement may with advantage be provided in awireless transceiver as well as in a radio transmission device such as awireless access point or a wireless terminal.

Thanks to the application of the quarter wave transforming element, thepower loss in the load modulation arrangement could be minimized on theat least one variable capacitive element, as the input impedance lookinginto the network is high and results in a low current and therefore asmall RF voltage over the tuning capacitor when the value of thecapacitor is large. If the capacitance on the at least one variablecapacitive element is small, it results in a low input impedance lookinginto the network and thus a large current and a large RF voltage swingover the tuning capacitor. However, in this situation the value of thetuning capacitor is small and thus the loss of power in the same issmall.

By using a T shape network in conjunction with a quarter wavetransforming element the problems with dynamic range and powerdissipation for T networks are solved. Thus a load modulationarrangement with a bandwidth far better than a Pi shaped network isachieved.

An advantage of the present device is that an improved efficiency isreached, which saves energy resources.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail in relationto the enclosed drawings, in which:

FIG. 1 a is a block diagram illustrating embodiments of a loadmodulation network.

FIG. 1 b is a block diagram illustrating some other embodiments of aload modulation network.

FIG. 2 is a block diagram illustrating embodiments of a wirelesscommunication network.

FIG. 3 is a block diagram illustrating embodiments of a method for loadmodulation.

DETAILED DESCRIPTION

The invention is defined as a load modulation arrangement which may beput into practice in the embodiments further described below.

FIG. 1 a illustrates a load modulation arrangement 100, such as a loadmodulation network, according to the present solution. The loadmodulation arrangement 100 may according to some embodiments berepresented by a T load modulation network. The load modulationarrangement 100 is adapted to be connected to an amplifying device (notshown). The amplifying device may be embodied by any arbitrary type ofamplifier, such as e.g. a power amplifier of class A, AB, B, C, D, E, For S, or hybrids between these or other classes of power amplifiers.However, the load modulation arrangement 100 may with certain advantagebe used for switched power amplifiers, such as amplifiers of class D, Eand F. The power amplifier has a power output which may be coupled tothe load modulation arrangement 100 in order to provide an amplifiedsignal to the load modulation arrangement 100.

The amplifying device may be based on or comprise a wide range oftransistors or switching units, such as e.g. Insulated Gate BipolarTransistor (IGBT), Metal—Oxide—Semiconductor Field-Effect Transistor(MOSFET), junction gate field-effect transistor (JFET), field-effecttransistor FET, LDMOS transistors, GaAs transistors, GaAs MESFET,bipolar junction transistor, Gallium-Nitride High Electron MobilityTransistor (GaN-HEMT), valves or PNP-transistors etc.

The load modulation arrangement 100 is further adapted to be connectedto a load 140. The load 140 may be resistive or may include bothresistance and reactance. The load 140 may further be fixed.

Also FIG. 1 b illustrates a load modulation arrangement 100, such as aload modulation network, according to the present solution. The loadmodulation arrangement 100 further comprises a first reactive element110, a second reactive element 120 and at least one variable capacitiveelement 130. The first reactive element 110 and/or the second reactiveelement 120 may be represented by an inductor, according to someembodiments as illustrated in FIG. 1 a. In some embodiments, the firstreactive element 110 and/or the second reactive element 120 may berepresented by a transmission line as illustrated in FIG. 1 b. Further,according to some embodiments, the first reactive element 110 and/or thesecond reactive element 120 may be represented by reactive elements ofdifferent types, such as e.g. one transmission line and one inductor.

The at least one variable capacitive element 130 may according to someembodiments be represented by a transistor output capacitance.

The at least one variable capacitive element 130 may according to someembodiments be a tunable capacitor or variable capacitor, e.g.comprising, as a non limiting example, a transistor output capacitance,a varactor, a Micro-Electro-Mechanical Systems (MEMS) capacitor or abarium strontium titanate tunable capacitance.

The at least one variable capacitive element 130 may according to someembodiments may comprise just one variable capacitive element 130. Theat least one variable capacitive element 130 may however according tosome other embodiments comprise a plurality of variable capacitiveelements 130, such as e.g. two variable capacitive elements 130.According to these embodiments, the plurality of variable capacitiveelements 130 may be connected e.g. in series or in parallel to thearrangement 100.

According to some embodiments, the load modulation arrangement 100 maybe adapted such that the voltage over the variable capacitive element130 decreases for increasing values of capacitance of the variablecapacitive element 130, and vice versa.

According to some embodiments, the load modulation arrangement 100 maybe adapted such that the RF voltage amplitude over the variablecapacitive element 130 decreases for increasing value of capacitance ofthe capacitive element 130, and vice versa.

According to some embodiments, the at least one variable capacitiveelement 130 may be represented by a barium-strontium-titanate tunablecapacitance. This technique is built on materials where the relativepermittivity of the dielectric is a function of applied bias voltage.This may also be used for a tunable quarter wave transforming element150.

However, according to some embodiments, the at least one variablecapacitive element 130 may comprise a transistor and/or a diode and/or aMicro-Electro-Mechanical Systems (MEMS) component and/or a variabledielectric material and/or a piezo-electrical device.

The at least one variable capacitive element 130 may according to someembodiments be represented by a varactor diode.

A Varactor or varicap is a diode in which the junction capacitance isused with the diode reverse biased. The junction capacitance may becontrolled by changing the reverse bias voltage. Depending on dopingprofile, the characteristics of the capacitance as a function of biasvoltage may be controlled. On die level, the quality factor of thevaractor is set by the series resistance where the size of the P-Njunction is one contributing factor.

The load modulation arrangement 100 comprises a quarter wavetransforming element 150 adapted to be connected to the first reactiveelement 110. The quarter wave transforming element 150 may according tosome embodiments be represented by a quarter wavelength transmissionline and may be used as e.g. an impedance inverter.

The quarter wave transforming element 150 is a device or circuit thattransforms its load impedance half a turn in the smith chart around thecharacteristic impedance of the transformer itself. Thus it has an inputimpedance inversely proportional to the load impedance. Thus thenormalized input impedance equals the normalized load admittance. Thequarter wave transforming element 150 may according to some embodimentscomprise a transmission line with the length set equal to λ/4, where λis the wave length.

This arrangement transforms the input impedance to:

${Zin} = \frac{Z^{2}}{Znet}$

Where Zin is the input impedance of the entire network 100, Znet is theimpedance looking into the network 100, without the quarter wavetransformer 150 and Z the characteristic impedance of the quarter wavetransformer 150.

According to some embodiments, the quarter wave transforming element 150is coupled in series with the first reactive element 110.

In some embodiments, the quarter wave transforming element 150 has acharacteristic impedance equal to the geometric mean value of theimpedance of the arrangement 100 without the quarter wave transformingelement 150, for the lowest and highest value of the variablecapacitance of the at least one variable capacitive element 130.

The characteristic impedance of the quarter wave transforming element150 may thus be chosen as the geometric mean value of the inputimpedance tuning range of network 100 less the quarter wave transformer.This choice inverts the input impedance in a symmetric manner mirroringthe high and low end of the tuning range.

The quarter wave transforming element 150 may according to someembodiments comprise a plurality of quarter wave transforming elements150.

According to some embodiments, the load modulation arrangement 100comprises the first reactive element 110 and the second reactive element120, coupled in series. Further, the load modulation arrangement 100 maycomprise the at least one variable capacitive element 130. The at leastone variable capacitive element 130 may be coupled to the first reactiveelement 110 and the second reactive element 120. Further, the quarterwave transforming element 150 may be coupled in series with the firstreactive element 110.

According to some embodiments, the load modulation arrangement 100comprises a T network.

A major advantage with using a quarter wave transforming element 150 inan arrangement 100 is the lower power dissipation in the tuning elementat high power levels.

According to some embodiments, the value of the first reactive element110 is selected such that the imaginary impedance of the arrangement 100is zero for the tuning range ends.

FIG. 2 depicts a first node 220 communicating with a second node 210 ina wireless communication network 200. The communication between thefirst node 220 and the second node 210 is made over a radio link 240 ina cell 250 comprised in the wireless communication network 200. Thewireless communication network 200 may also comprise a radio networkcontroller 230.

The first node 220 and the second node 210 may both be referred to asradio transmission devices. In some embodiments, the first node 220 maybe represented by a base station, a wireless communications station, afixed station, a control station, a repeater or any similar arrangementfor radio communication. The second node 210 may in some embodiments berepresented by a user equipment such as a mobile cellularradiotelephone, a Personal Digital Assistant (PDA), a laptop, a computeror any other kind of device capable of communicate radio resources.

The wireless communication network 200 may be based on technologies suchas e.g. Code division multiple access (CDMA), Wideband Code DivisionMultiple Access (WCDMA), CDMA 2000, High Speed Downlink Packet DataAccess (HSDPA), High Speed Uplink Packet Data Access (HSUPA), High DataRate (HDR) etc.

Any or both of the radio transmission devices 210, 220 may comprise atleast one load modulation arrangement 100 for load modulation of signalsaccording to the present arrangement 100. The radio transmission devices210, 220 may be e.g. a wireless access point 220 or a wireless terminal210.

The load modulation arrangement 100 as herein described may howeveralternatively be provided in an arbitrary electronic device whereinthere appear a need of load modulation of signals, such as a hearingaid, wireless speakers, notebook computers, walkie-talkies, huntingradios, baby monitors etc.

An advantage of the present arrangement 100 may be that it provides aload modulation network which is uncomplicated to implement.

Another advantage of the present load modulation arrangement 100 is thatit may increase the efficiency of a power amplifier at backed offconditions, at least regarding the output power.

FIG. 3 schematically illustrates a method for load modulation accordingto some embodiments. The load modulation is performed in an arrangement100. The arrangement 100 is adapted to be connected to an amplifyingdevice. The load modulation arrangement 100 comprises a first reactiveelement 110, a second reactive element 120 and at least one variablecapacitive element 130. Also, the method comprises the further step ofconnecting 310 a quarter wave transforming element 150 to the firstreactive element 110.

The present load modulation arrangement 100 may further be designed by amethodology comprising four steps:

Step 1

Determine the maximum usable range of capacitance of the at least onevariable capacitive element 130.

Step 2

Select the second reactive element 120 to set the dynamic range of theimpedance seen looking into the network 100. The real impedancetransformation is only dependant on the values of the at least onevariable capacitive element 130 and the reactive element 120.

Step 3

Select the first reactive element 110 to make the impedance seen lookinginto the network 100 purely resistive, for the endpoints of the tuningrange i.e. when the at least one variable capacitive element 130 highestand lowest value.

Step 4

Compute the geometric mean of the impedance seen into the network 100without the quarter wave transformer 150, for the largest and smallestvalue of the tunable capacitance of the at least one variable capacitiveelement 130. This value may with certain advantage be used for thecharacteristic impedance of the quarter wave transformer.

The present arrangement 100 relates to a load modulation network thatmay be used advantageously for wireless communication in a plurality ofcommunication situations in a wireless communication network.

While the load modulation arrangement 100 described in this document issusceptible to various modifications and alternative forms, specificembodiments thereof are shown by way of example in the drawings and areherein described in detail. It should be understood, however, that thereis no intent to limit the present arrangement 100 to the particularforms disclosed, but on the contrary, the present device is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the load 35 modulation arrangement 100 as defined by theclaims.

Like reference numbers signify like elements throughout the descriptionof the figures.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless expressly stated otherwise. Itshould be further understood that the terms “comprises” and/or“comprising” when used in this specification is taken to specify thepresence of stated features, integers, steps, operations, elements,and/or components, but does not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. It will be understood that when anelement is referred to as being “connected” or “coupled” to anotherelement, it can be directly connected or coupled to the other element orintervening elements may be present.

Furthermore, “connected” or “coupled” as used herein may includewirelessly connected or coupled. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

Unless otherwise defined, all terms including technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which these methods and arrangementsbelongs. It will be further understood that terms, such as those definedin commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand will not be interpreted in an idealized or overly formal senseunless expressly so defined herein.

1. A load modulation arrangement adapted to be connected to anamplifying device, said load modulation arrangement comprising: a firstreactive element, a second reactive element and at least one variablecapacitive element and a quarter wave transforming element to connect tothe first reactive element.
 2. The load modulation arrangement accordingto claim 1, where the quarter wave transforming element is coupled inseries with the first reactive element.
 3. The load modulationarrangement according to claim 1, where the quarter wave transformingelement has a characteristic impedance equal to a geometric mean valueof an impedance of the load modulation arrangement, without the quarterwave transforming element, for a lowest and highest value, respectively,of a variable capacitance of the at least one variable capacitiveelement.
 4. The load modulation arrangement (100) according to claim 1,where a value of the first reactive element is selected such that animaginary impedance of the load modulation arrangement is zero for endsof a tuning range.
 5. The load modulation arrangement according to claim1, where at least one of the first reactive element or the secondreactive element is represented by an inductor.
 6. The load modulationarrangement according to claim 1, where at least one of the firstreactive element or the second reactive element is represented by atransmission line.
 7. The load modulation arrangement according to claim1, where the at least one variable capacitive element is represented bya transistor output capacitance.
 8. The load modulation arrangementaccording to claim 1, where the at least one variable capacitive elementis represented by a varactor diode.
 9. The load modulation arrangementaccording to claim 1, where a Radio Frequency (RF) voltage amplitudeover the variable capacitive element decreases for increasing values ofcapacitance of the capacitive element, and where the RF voltageamplitude over the variable capacitive element increases for decreasingvalues of capacitance of the capacitive element.
 10. The load modulationarrangement according to claim 1, where the load modulation arrangementcomprises a T network.
 11. A method for load modulation in anarrangement adapted to be connected to an amplifying device, the methodcomprising: providing a first reactive element, a second reactiveelement and at least one variable capacitive element, and connecting aquarter wave transforming element to the first reactive element.
 12. Aradio transmission device comprising: at least one load modulationarrangement including: a first reactive element, a second reactiveelement, at least one variable capacitive element, and a quarter wavetransforming element to connect to the first reactive element.
 13. Theradio transmission device according to claim 12, where the radiotransmission device is a wireless access point.
 14. The radiotransmission device according to claim 12, where the radio transmissiondevice is a wireless terminal.
 15. The radio transmission deviceaccording to claim 12, where the quarter wave transforming element iscoupled in series with the first reactive element.
 16. The radiotransmission device according to claim 12, where the quarter wavetransforming element has a characteristic impedance equal to a geometricmean value of an impedance of the load modulation arrangement, withoutthe quarter wave transforming element, for a lowest and highest value,respectively, of a variable capacitance of the at least one variablecapacitive element.
 17. The radio transmission device according to claim12, where a value of the first reactive element is selected such that animaginary impedance of the load modulation arrangement is zero for endsof a tuning range.
 18. The radio transmission device according to claim12, where at least one of the first reactive element or the secondreactive element is represented by an inductor.
 19. The radiotransmission device according to claim 12, where at least one of thefirst reactive element or the second reactive element is represented bya transmission line.
 20. The radio transmission device according toclaim 12, where the at least one variable capacitive element isrepresented by a transistor output capacitance.